Search

SSCI-VIDE+CARE+PVE:ACV; International audience; Ethylene oxide (EO) is nowadays a chemical intermediate of paramount importance. As one of the highest volume petrochemicals, it serves as a precursor for the further production of added value molecules, including plastics, polyester and ethylene glycol. EO is industrially produced by the partial oxidation (epoxidation) of ethylene with air (or oxygen) on Ag/α-Al2O3 catalysts at low reaction temperatures (around 220 oC) and high pressures (10-30 bar). Silver is the only one known active heterogeneous catalyst for the epoxidation of ethylene. The epoxidation is in competition with the combustion side reactions of both ethylene and EO, leading to the production of CO2 and H2O. The mechanism of the epoxidation and, in particular the nature of the involved oxygen species are under debate. We have designed by reactive magnetron sputtering a solid oxide electrochemical cell based on nanostructured Ag/Gadolinia-Doped Ceria (a well-known O2- conductor) catalyst. We found an unprecedent linear increase of the selectivity towards EO (Fig. 1) and of the ethylene conversion. These results demonstrate that EO can be electrocatalytically produced in a solid oxide electrochemical cell between 220 °C and 300 °C on a nanostructured Ag/GDC electrocatalyst prepared by reactive magnetron sputtering. Despite low values of Faradaic efficiencies, the EO selectivity and the ethylene conversion can be increased at 220 °C with the application of small positive currents (< 1 mA) that correspond to an energy consumption of around ~ 1 mW/cm². This proof-of-concept opens the way for a new environmentally-friendly route (without utilization of chlorinated hydrocarbons) for the epoxidation of ethylene in a solid oxide cell via direct electrooxidation of ethylene. These results also underline the key role of O2- species in the mechanism of ethylene epoxidation on Ag.

International audience; In this paper, vanadium nitride (VN) thin films have been deposited on Al substrates by reactive magnetron sputtering. Thermochromic VO 2 films have been obtained by air oxidation of VN samples performed at three temperatures (450, 525 and 550 C) at various durations (lower than 50 min). X-ray diffraction and Raman spectrometry of the VN oxidized films indicate that VO 2 and V 2 O 5 are the only phases produced during the oxidation process. Vanadium dioxide is the first oxide formed. It coexists with VN in a long period at 450 C or suddenly disappears at 525 and 550 C. Whatever the temperature, V 2 O 5 is exclusively detected after the total oxidation of VN. This oxide is detrimental to the thermochromic performance of films. The emissivity-switching properties of the oxidized films were analyzed by infrared camera in the 7.5e13 mm range. The comparison among all the samples exhibiting a thermochromic behavior shows that the maximum emissivity switch is independent of the oxidation temperature and the surface morphology of the samples. These results could open a new strategy in the investigation of VN oxidation as a method to obtain VO 2 , along with an insight into the correlation between surface morphology and optical properties.

In this work, we report the self-assembled growth of vertically aligned columnar Cu2O + Cu4O3 nanocomposite thin films on glass and silicon substrates by reactive sputtering at room temperature. Microstructure analyses show that each phase in nanocomposite films has the columnar growth along the whole thickness, while each column exhibits the single phase characteristics. The local epitaxial growth behavior of Cu2O is thought to be responsible for such an unusual microstructure. The intermediate oxygen flow rate between those required to synthesize single phase Cu2O and Cu4O3 films produces some Cu2O nuclei, and then the local epitaxial growth provides a strong driving force to promote Cu2O nuclei to grow sequentially, giving rise to Cu2O columns along the whole thickness. Lower resistivity has been observed in such kind of nanocomposite thin films than that in single phase thin films, which may be due to the interface coupling between Cu2O and Cu4O3 columns.

International audience; Considered a major issue in citrus growing, Huanglongbing (HLB), also known as Citrus Greening or yellow dragon disease, is a citrus bacterial disease. This disease is caused by the bacteria Candidatus Liberibacter spp that is spread by Diaphorina citri, also called citrus psylla. This stinging insect allows a rapid spread of tree disease trees by feeding on the leaf petiole. In the short term, the HLB causes a decline and the death of trees. In Brazil and Florida, the disease affects several million trees and thou-sands of hectares have had to be torn down. This disease affects the entire Caribbean basin including Guadeloupe and Martinique. After the bite leading to HLB infection, the reaction of the plant will result in the synthesis of callose in the pores of the phloem sieve cells thus leading to a stop of elaborated sap flow. Today, there is no pure resistance to HLB within the Citrus genus. However, the Tahiti limer (natu-ral triploid variety, 3x) is much less affected by the disease (Gomez, 2008), other diploid varieties (2x) being very sensitive. Our study was to decipher the potential traits of tolerance to HLB related to poly-ploidy. Diploid (2x, Citrus aurantiifolia) and triploid (3x, Citrus latifolia) limes grafted onto diploid citru-melo 4475 (Citrus paradisi × Poncirus trifoliata) rootstocks were investigated when naturally infected by HLB or infected by grafting. The plant physiology, the anatomy, of leaf petiole were analyzed using Scanning Electron Microscope to observe callose deposition at sieve plate of the phloem, as well leaf starch content and detoxification enzyme activities in 2x and 3x leaves were investigated. The results of these experiments seem to show that 3x are more tolerant than 2x.

This paper reports on the first study of chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. Thin films were deposited in a Ar/O2/N2 mixture as reactive plasma, from two elemental La and Fe targets, at room and high temperature (25 and 800°C). Films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. Oxynitride properties were investigated and compared to oxide films deposited in Ar/O2 gas mixture. All oxide and oxynitride films present an orthorhombic structure. However, nitrogen doping limited to 1-1.5% leads to lattice expansion (4%), bandgap narrowing, a lower electrical resistivity in range [25-350°C] , and modification of Infrared and Raman spectra. Electron Energy Loss Spectroscopy measurements clearly show the presence of two nitrogen sites with an “active” intra-granular nitrogen associated to an enhancement of the physical properties.